Origin of anti-Mullerian hormone in bovine freemartin fetuses

Age-specific analysis of anti-müllerian hormone and liver biochemical parameters in freemartin holstein calves and heifers: A pilot study

Freemartinism is the most common congenital anomaly among sexual disorders in dairy cows. This syndrome typically occurs in different-sex twin pregnancies and causes vascular anastomoses to form with the placenta in the early stages of fetal development. The study aims to determine the effectiveness of Anti-müllerian hormone (AMH) levels in calves and heifers of different age groups for diagnostic factors and to investigate the potential consequences of different hormone levels in different age groups on some liver biochemical parameters. The study involved 50 cattle from diverse age categories, divided into the freemartin group (FM Group, n=25) and the control group (C Group, n=25). Both FM and control groups were further divided into early-age (3-5 months), middle-aged (5-9 months), and older-aged groups (9-12 months). Serum AMH levels, along with total protein, albumin, and total cholesterol levels, were measured. While no statistically significant difference in AMH levels was observed in the early-age group (P:0.53), significant differences were determined in the middle (P:0.015) and older-age groups (P:0.01), where the FM group exhibited significantly decreased AMH levels compared to the control group. The evaluation of liver biochemistry revealed a statistically significant difference in total protein levels between the FM and control groups in the older age group (P:0.033). Consequently, it is reasonable to suggest that AMH levels may serve as a valid parameter for diagnosing freemartin syndrome in calves aged older than five months. Conversely, particularly in young calves, no significant differences in liver functionality were observed between freemartin-affected and healthy calves.

Somatic cell fate maintenance in mouse fetal testes via autocrine/paracrine action of AMH and activin B

Fate determination and maintenance of fetal testes in most mammals occur cell autonomously as a result of the action of key transcription factors in Sertoli cells. However, the cases of freemartin, where an XX twin develops testis structures under the influence of an XY twin, imply that hormonal factor(s) from the XY embryo contribute to sex reversal of the XX twin. Here we show that in mouse XY embryos, Sertoli cell-derived anti-Mullerian hormone (AMH) and activin B together maintain Sertoli cell identity. Sertoli cells in the gonadal poles of XY embryos lacking both AMH and activin B transdifferentiate into their female counterpart granulosa cells, leading to ovotestis formation. The ovotestes remain to adulthood and produce both sperm and oocytes, although there are few of the former and the latter fail to mature. Finally, the ability of XY mice to masculinize ovaries is lost in the absence of these two factors. These results provide insight into fate maintenance of fetal testes through the action of putative freemartin factors.

Low prevalence of male microchimerism in women with Mayer-Rokitansky-Küster-Hauser syndrome

STUDY QUESTION

Is there an increased prevalence of male microchimerism in women with Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome, as evidence of fetal exposure to blood and anti-Müllerian hormone (AMH) from a (vanished) male co-twin resulting in regression of the Müllerian duct derivatives?

SUMMARY ANSWER

Predominant absence of male microchimerism in adult women with MRKH syndrome does not support our hypothesis that intrauterine blood exchange with a (vanished) male co-twin is the pathophysiological mechanism.

WHAT IS KNOWN ALREADY

The etiology of MRKH is unclear. Research on the phenotype analogous condition in cattle (freemartinism) has yielded the hypothesis that Müllerian duct development is inhibited by exposure to AMH in utero. In cattle, the male co-twin has been identified as the source for AMH, which is transferred via placental blood exchange. In human twins, a similar exchange of cellular material has been documented by detection of chimerism, but it is unknown whether this has clinical consequences.

STUDY DESIGN, SIZE, DURATION

An observational case–control study was performed to compare the presence of male microchimerism in women with MRKH syndrome and control women. Through recruitment via the Dutch patients’ association of women with MRKH (comprising 300 members who were informed by email or regular mail), we enrolled 96 patients between January 2017 and July 2017. The control group consisted of 100 women who reported never having been pregnant.

PARTICIPANTS/MATERIALS, SETTING, METHODS

After written informed consent, peripheral blood samples were obtained by venipuncture, and genomic DNA was extracted. Male microchimerism was detected by Y-chromosome–specific real-time quantitative PCR, with use of DYS14 marker. Possible other sources for microchimerism, for example older brothers, were evaluated using questionnaire data.

MAIN RESULTS AND THE ROLE OF CHANCE

The final analysis included 194 women: 95 women with MRKH syndrome with a mean age of 40.9 years and 99 control women with a mean age of 30.2 years. In total, 54 women (56.8%) were identified as having typical MRKH syndrome, and 41 women (43.2%) were identified as having atypical MRKH syndrome (when extra-genital malformations were present). The prevalence of male microchimerism was significantly higher in the control group than in the MRKH group (17.2% versus 5.3%, P = 0.009). After correcting for age, women in the control group were 5.8 times more likely to have male microchimerism (odds ratio 5.84 (CI 1.59–21.47), P = 0.008). The mean concentration of male microchimerism in the positive samples was 56.0 male genome equivalent per 1 000 000 cells. The prevalence of male microchimerism was similar in women with typical MRKH syndrome and atypical MRKH syndrome (5.6% versus 4.9%, P = 0.884). There were no differences between women with or without microchimerism in occurrence of alternative sources of XY cells, such as older brothers, previous blood transfusion, or history of sexual intercourse.

LIMITATIONS, REASON FOR CAUTION

We are not able to draw definitive conclusions regarding the occurrence of AMH exchange during embryologic development in women with MRKH syndrome. Our subject population includes all adult women and therefore is reliant on long-term prevalence of microchimerism. Moreover, we have only tested blood, and, theoretically, the cells may have grafted anywhere in the body during development. It must also be considered that the exchange of AMH may occur without the transfusion of XY cells and therefore cannot be discovered by chimerism detection.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to test the theory that freemartinism causes the MRKH syndrome in humans. The study aimed to test the presence of male microchimerism in women with MRKH syndrome as a reflection of early fetal exposure to blood and AMH from a male (vanished) co-twin. We found that male microchimerism was only present in 5.3% of the women with MRKH syndrome, a significantly lower percentage than in the control group (17.2%). Our results do not provide evidence for an increased male microchimerism in adult women with MRKH as a product of intrauterine blood exchange. However, the significant difference in favor of the control group is of interest to the ongoing discussion on microchimeric cell transfer and the possible sources of XY cells.

STUDY FUNDING/COMPETING INTEREST(S)

None.

TRIAL REGISTRATION NUMBER

Dutch trial register, NTR5961.

Chimerism in health and potential implications on behavior: A systematic review

In this review, we focus on the phenomenon of chimerism and especially microchimerism as one of the currently underexplored explanations for differences in health and behavior. Chimerism is an amalgamation of cells from two or more unique zygotes within a single organism, with microchimerism defined by a minor cell population of <1%. This article first presents an overview of the primary techniques employed to detect and quantify the presence of microchimerism and then reviews empirical studies of chimerism in mammals including primates and humans. In women, male microchimerism, a condition suggested to be the result of fetomaternal exchange in utero, is relatively easily detected by polymerase chain reaction molecular techniques targeting Y-chromosomal markers. Consequently, studies of chimerism in human diseases have largely focused on diseases with a predilection for females including autoimmune diseases, and female cancers. We detail studies of chimerism in human diseases and also discuss some potential implications in behavior. Understanding the prevalence of chimerism and the associated health outcomes will provide invaluable knowledge of human biology and guide novel approaches for treating diseases.

[Relationship of the ovarian reserve with autoimmune thyroid diseases in the reproductive period]

AIM

To compare ovarian reserve in healthy women of reproductive age - carriers of antithyroid antibodies (ATA) and in healthy women of reproductive age negative for ATA.

MATERIALS AND METHODS

70 healthy women of young reproductive age in the state of euthyroidism (from 18 to 38 years old) were examined. Participants were divided into equal groups (n=35) depending on the status of the presence of antithyroid antibodies (AT-TPO, AT-TG). On the 2nd-4th days of the menstrual cycle, the following markers of the ovarian reserve were determined: serum levels of anti-Müllerian hormone (AMG), inhibin B, FSH, LH, estradiol, testosterone and progesterone, as well as ultrasound parameters - the number of antral follicles and the volume of the ovaries. In addition, to determine the predisposition to premature ovarian failure, an analysis was performed to the number of CGG repeats in the FMR1 gene.

RESULTS AND DISCUSSION

Statistically significantly differs such parameters as the level of estradiol and testosterone, while the differences were not clinically significant. All the parameters evaluated were within the normal range, the main predictors of the ovarian reserve (levels of AMG and inhibin B, the number of antral follicles) remained in the normal range. An increase in the number of repeats of CGG in the FMR1 gene was not detected in any of the participants in the study.

CONCLUSION

In healthy young reproductive age women, the status of ATA does not have a direct effect on the ovarian reserve.

Anti-Müllerian Hormone in Fertility Preservation: Clinical and Therapeutic Applications

Anti-Müllerian hormone (AMH) is a member of the transforming growth factor (TGF)-beta family and a key regulator of sexual differentiation and folliculogenesis. While the serum AMH level has been used in reproductive medicine as a biomarker of quantitative ovarian reserve for more than 20 years, new potential therapeutic applications of recombinant AMH are emerging, notably in the field of oncofertility. Indeed, it is well known that chemotherapy, used to treat cancer, induces ovarian follicular depletion and subsequent infertility. Animal models have been used widely to understand the effects of different cytotoxic agents on ovarian function, and several hypotheses regarding chemotherapy gonadotoxicity have been proposed, that is, it might have a direct detrimental effect on the primordial follicles constituting the ovarian reserve and/or on the pool of growing follicles secreting AMH. Recently, a new mechanism of chemotherapy-induced follicular depletion, called the “burn-out effect,” has been proposed. According to this theory, chemotherapeutic agents may lead to a massive growth of dormant follicles which are then destroyed. As AMH is one of the factors regulating the recruitment of primordial follicles from the ovarian reserve, recombinant AMH administration concomitant with chemotherapy might limit follicular depletion, therefore representing a promising option for preserving fertility in women suffering from cancer. This review reports on the potential usefulness of AMH measurement as well as AMH’s role as a therapeutic agent in the field of female fertility preservation.

Twinning rate in buffaloes: A case report

The information of twin pregnancy frequencies in buffaloes is scarce in the literature. Evidence even indicates that twin pregnancies are not carried to term, but it does not seem to be the case. In this case report, the event of twin pregnancy in buffaloes is reported as well as its frequency. Twin birth is the presence of two or more embryos in a single gestation. Multiple births are uncommon in buffaloes since the species is uniparous. We studied a population of Murrah buffaloes in which slightly more than 13,000 births were observed. In this study, the frequency of occurrence of twin births in Murrah buffaloes was 0.14%. This low incidence impaired the estimation of genetic parameters. Twins can have advantages and disadvantages depending on the production system, which are discussed in this case report.

The bovine anterior hypothalamus: Characterization of the vasopressin-oxytocin containing nucleus and changes in relation to sexual differentiation

In an effort to systematically describe the neurochemical anatomy of the bovine anterior hypothalamus, we used a series of immunocytochemical markers such as acetylcholine esterase (AChE), arginine-vasopressin (AVP), calbindin (Calb), galanin (Gal), neuropeptide-Y (NPY), oxytocin (OXT), somatostatin (SST), and vasoactive intestinal peptide (VIP). We also investigated the potential sex difference present in the suprachiasmatic nucleus (SCN) and the vasopressin-oxytocin containing nucleus (VON) of six male and six female Bos taurus. Our study revealed that the cytochemical structure of the cattle anterior hypothalamus follows the blueprint of other mammals. The VON, which was never described before in cattle, showed a sex difference with a 33.7% smaller volume and 23.2% fewer magnocellular neurons (approximately 20-30 μm) in the male. The SCN also did show a sex difference in VIP neurons and volume with a 36.1% larger female nucleus with 28.1% more cells. Additionally, we included five heifers with freemartin syndrome as a new animal model relevant to sexual differentiation in the brain. This is, to the best of our knowledge, the first freemartin study in relation to the brain. Surprisingly, the SCN of freemartin heifers was 32.5% larger than its control male and female counterparts with 29% more VIP cells. Conversely, the freemartin VON had an intermediary size between male and female. To analyze our data, a classical statistical analysis and a novel multivariate and multi-aspect approach were applied. These findings shed new light on sexual dimorphism in the bovine brain and present this species with freemartins as a valuable animal model in neuroscience.

Fetal sex alters maternal anti-Mullerian hormone during pregnancy in cattle

Anti-Mullerian hormone (AMH) is expressed by both male and female fetuses during mammalian development, with males expressing AMH earlier and at significantly higher concentration. The aim of the current study was to explore the potential impact of pregnancy and fetal sex on maternal AMH and to determine if plasma (Pl) AMH or placenta intercotyledonary membrane and cotyledonary AMH receptor 2 (AMHR2) mRNA expression differ in pregnant cows carrying male vs. female fetuses. AMH levels in blood were measured using a bovine optimized ELISA kit. Cows pregnant with a male fetus were observed to have a significantly greater difference in Pl AMH between day 35 and 135 of gestation. Average fetal AMH level between 54 and 220days of gestation was also observed to be significantly higher in male vs. female fetuses. Intercotyledonary membranes and cotyledons were found to express AMHR2 between days 38 and 80 of gestation at similar levels in both fetal sexes. These findings support the hypothesis that fetal sex alters maternal Pl AMH during pregnancy in cattle.

Age-associated and deslorelin-induced declines in serum anti-Müllerian hormone concentrations in female cheetahs, Acinonyx jubatus

Anti-Müllerian hormone (AMH) is widely used in human medicine to non-invasively estimate the size of the ovarian follicle reserve and to predict the ovarian response to gonadotropin stimulation in the context of assisted reproductive technologies (e.g., IVF). These applications of AMH testing have recently expanded to non-human mammals, with production animals, such as cows, goats and sheep being the primary focus of AMH research. However, few investigations have involved exotic species, and in particular carnivores. In this study, we measured AMH concentrations (0.078-3.078ng/mL) in archived serum samples that had been collected from 36 adult female cheetahs across their reproductive lifespan (2-15years of age). Similar to other mammals, AMH concentration in cheetahs declined with age, and its variability among females of the same age was considerable. The rates at which AMH declined over time in individual cheetahs were also highly variable. Five cheetahs had been contracepted with the long-acting GnRH agonist deslorelin for 6-18months prior to sample collection, and their AMH concentrations were relatively low compared to untreated females. In this first study of AMH in an exotic carnivore, the findings demonstrate that the age-associated decline in AMH is highly variable and that deslorelin appears to suppress AMH concentration in serum. Owing to the increased use of assisted reproductive technologies in ex situ populations of threatened and endangered species, such as cheetahs, the present study's findings will need to be taken into consideration if AMH is to be used successfully to optimize breeding management decisions in exotic species.

Hydrogen-rich Water Exerting a Protective Effect on Ovarian Reserve Function in a Mouse Model of Immune Premature Ovarian Failure Induced by Zona Pellucida 3

Background:

Premature ovarian failure (POF) is a disease that affects female fertility but has few effective treatments. Ovarian reserve function plays an important role in female fertility. Recent studies have reported that hydrogen can protect male fertility. Therefore, we explored the potential protective effect of hydrogen-rich water on ovarian reserve function through a mouse immune POF model.

Methods:

To set up immune POF model, fifty female BALB/c mice were randomly divided into four groups: Control (mice consumed normal water, n = 10), hydrogen (mice consumed hydrogen-rich water, n = 10), model (mice were immunized with zona pellucida glycoprotein 3 [ZP3] and consumed normal water, n = 15), and model-hydrogen (mice were immunized with ZP3 and consumed hydrogen-rich water, n = 15) groups. After 5 weeks, mice were sacrificed. Serum anti-Müllerian hormone (AMH) levels, granulosa cell (GC) apoptotic index (AI), B-cell leukemia/lymphoma 2 (Bcl-2), and BCL2-associated X protein (Bax) expression were examined. Analyses were performed using SPSS 17.0 (SPSS Inc., Chicago, IL, USA) software.

Results:

Immune POF model, model group exhibited markedly reduced serum AMH levels compared with those of the control group (5.41 ± 0.91 ng/ml vs. 16.23 ± 1.97 ng/ml, P = 0.033) and the hydrogen group (19.65 ± 7.82 ng/ml, P = 0.006). The model-hydrogen group displayed significantly higher AMH concentrations compared with that of the model group (15.03 ± 2.75 ng/ml vs. 5.41 ± 0.91 ng/ml, P = 0.021). The GC AI was significantly higher in the model group (21.30 ± 1.74%) than those in the control (7.06 ± 0.27%), hydrogen (5.17 ± 0.41%), and model-hydrogen groups (11.24 ± 0.58%) (all P < 0.001). The GC AI was significantly higher in the model-hydrogen group compared with that of the hydrogen group (11.24 ± 0.58% vs. 5.17 ± 0.41%, P = 0.021). Compared with those of the model group, ovarian tissue Bcl-2 levels increased (2.18 ± 0.30 vs. 3.01 ± 0.33, P = 0.045) and the Bax/Bcl-2 ratio decreased in the model-hydrogen group.

Conclusions:

Hydrogen-rich water may improve serum AMH levels and reduce ovarian GC apoptosis in a mouse immune POF model induced by ZP3.

Unusual Twinning Resulting in Chimerism: A Systematic Review on Monochorionic Dizygotic Twins

Traditionally, it is understood that dizygotic (DZ) twins always have a dichorionic placenta. However, with 8% blood chimerism in DZ twins, placental sharing is probably more common than previously has been recognized. In this article, we will review all available cases of monochorionic dizygotic (MCDZ) twins. A total of 31 twins have been described in literature. A monochorionic diamniotic placenta is reported in all cases. Assisted reproductive technology is responsible for the origin of the pregnancy in 82.1% of the cases. In 15.4% of the sex-discordant twins, a genital anomaly was reported in one of the twins. Chimerism is demonstrable in 90.3% of the twins, leading to various diagnostic difficulties. As this review shows that most MCDZ twins are discovered by accident, it can be argued that it is far more common than has been assumed until now. However, the prevalence is still unclear. Awareness of MCDZ twinning is important, with subsequently correct medical strategies. Similarly, the resulting (blood) chimerism is essential to consider in diagnostic procedures, pre- and postnatally. More research on the effect of placental transfusion between sex-discordant twins is required.

Overexpression of Anti-Müllerian Hormone Disrupts Gonadal Sex Differentiation, Blocks Sex Hormone Synthesis, and Supports Cell Autonomous Sex Development in the Chicken

The primary role of Anti-Müllerian hormone (AMH) during mammalian development is the regression of Müllerian ducts in males. This highly conserved function is retained in birds and is supported by the high levels of AMH expression in developing testes. Mammalian AMH expression is regulated by a combination of transcription factors, the most important being Sry-type high-mobility-group box transcription factor-9 (SOX9). In the chicken embryo, however, AMH mRNA expression precedes that of SOX9, leading to the view that AMH may play a more central role in avian testicular development. To define its role in chicken gonadal development, AMH was overexpressed using the RCASBP viral vector. AMH caused the gonads of both sexes to develop as small and undeveloped structures at both embryonic and adult stages. Molecular analysis revealed that although female gonads developed testis-like cords, gonads lacked Sertoli cells and were incapable of steroidogenesis. A similar gonadal phenotype was also observed in males, with a complete loss of both Sertoli cells, disrupted SOX9 expression and gonadal steroidogenesis. At sexual maturity both sexes showed a female external phenotype but retained sexually dimorphic body weights that matched their genetic sexes. These data suggest that AMH does not operate as an early testis activator in the chicken but can affect downstream events, such as sex steroid hormone production. In addition, this study provides a unique opportunity to assess chicken sexual development in an environment of sex hormone deficiency, demonstrating the importance of both hormonal signaling and direct cell autonomous factors for somatic sex identity in birds.

Anti-Müllerian Hormone Is Required for Chicken Embryonic Urogenital System Growth but Not Sexual Differentiation

In mammals, the primary role of anti-Müllerian hormone (AMH) during development is the regression of Müllerian ducts in males. These structures otherwise develop into fallopian tubes, oviducts, and upper vagina, as in females. This highly conserved function is retained in birds and is supported by the high levels of AMH expression in developing testes. In mammals, AMH expression is controlled partly by the transcription factor, SOX9. However, in the chicken, AMH mRNA expression precedes that of SOX9 , leading to the view that AMH may lie upstream of SOX9 and play a more central role in avian testicular development. To help define the role of AMH in chicken gonad development, we suppressed AMH expression in chicken embryos using RNA interference. In males, AMH knockdown did not affect the expression of key testis pathway genes, and testis cords developed normally. However, a reduction in the size of the mesonephros and gonads was observed, a phenotype that was evident in both sexes. This growth defect occurred as a result of the reduced proliferative capacity of the cells of these tissues, and male gonads also had a significant reduction in germ cell numbers. These data suggest that although AMH does not directly contribute to testicular or ovarian differentiation, it is required in a sex-independent manner for proper cell proliferation and urogenital system growth.

Anti-Müllerian hormone as a marker of premature ovarian aging in autoimmune thyroid disease

There is an increased incidence of autoimmune thyroid disease (AITD) in women with infertility. We hypothesized that serum anti-Müllerian hormone (AMH) levels will be lower in premenopausal women with AITD than controls. We evaluated ovarian reserve in women with AITD (n = 85) and healthy controls (n = 80), all <40 years old. Detailed data on reproductive history were obtained. Gonadotrophins, steroids, AMH, and inhibin B levels were measured during the follicular phase. The number of pregnancies as well as live births was lower in women with AITD (p < 0.01). No difference was observed in terms of FSH, estradiol, and inhibin B. AMH levels were lower in AITD women than in controls (1.16 + 0.17 versus 1.28 + 0.25 ng/ml, mean + SD, p = 0.001). According to the multiple regression analysis, even after age adjustment, AITD was significantly and independently affected AMH levels (t = 2.674, p = 0.008). Women with AITD seem to have a diminished ovarian follicular reserve and measurement of serum AMH level has the potential to be used to predict this comorbidity.

[What's new in 2014 about anti-Müllerian hormone?]

The existence of the anti-Müllerian hormone (AMH) has been postulated by Professor Alfred Jost to explain the regression of the Müllerian ducts during male sexual differentiation. Since then, AMH has been purified, its gene and specific receptor, AMHR-II have been cloned. Further, the signaling pathways were identified and it has been observed that AMH was produced by the granulosa cells of growing follicles. From the 2000s, unexpected roles of AMH have been highlighted, reactivating international research on this hormone. It is now well established that AMH plays a key role in the follicular recruitment and development. Over the past years, serum AMH measurements have been proposed as a marker of the follicular ovarian status, and a predictor of assisted reproductive cycles. AMH is also useful to assess the effectiveness of treatment of some gynecological tumors. This article is a review of the past five years advances on the regulation of the expression of AMH and its specific receptor AMHR-II in female.

Identification, expression, and regulation of anti-Müllerian hormone type-II receptor in the embryonic chicken gonad

Anti-Müllerian hormone (AMH) signaling is required for proper development of the urogenital system in vertebrates. In male mammals, AMH is responsible for regressing the Müllerian ducts, which otherwise develop into the fallopian tubes, oviducts, and upper vagina of the female reproductive tract. This role is highly conserved across higher vertebrates. However, AMH is required for testis development in fish species that lack Müllerian ducts, implying that AMH signaling has broader roles in other vertebrates. AMH signals through two serine/threonine kinase receptors. The primary AMH receptor, AMH receptor type-II (AMHR2), recruits the type I receptor, which transduces the signal intracellularly. To enhance our understanding of AMH signaling and the potential role of AMH in gonadal sex differentiation, we cloned chicken AMHR2 cDNA and examined its expression profile during gonadal sex differentiation. AMHR2 is expressed in the gonads and Müllerian ducts of both sexes but is more strongly expressed in males after the onset of gonadal sex differentiation. In the testes, the AMHR2 protein colocalizes with AMH, within Sertoli cells of the testis cords. AMHR2 protein expression is up-regulated in female embryos treated with the estrogen synthesis inhibitor fadrozole. Conversely, knockdown of the key testis gene DMRT1 leads to disruption of AMHR2 expression in the developing seminiferous cords of males. These results indicate that AMHR2 is developmentally regulated during testicular differentiation in the chicken embryo. AMH signaling may be important for gonadal differentiation in addition to Müllerian duct regression in birds.

Novel gonadal characteristics in an aged bovine freemartin

The gonads from a five-year-old freemartin Holstein animal were subjected to morphological analysis and to immunohistochemistry using antibodies against developmental and functional markers. We demonstrate, for the first time, the retention of anti-mullerian hormone (AMH) producing intratubular cells (Sertoli cells) in the context of abundant steroidogenic interstitial cells, and structures consistent with clusters of luteal cells. This novel report describes the clinical, gross and histological findings accompanying this newly described gonadal immunophenotype, and its implication in the understanding of freemartin development.

Evidence for almost complete sex-reversal in bovine freemartin gonads: formation of seminiferous tubule-like structures and transdifferentiation into typical testicular cell types

During mammalian sex determination of XY fetuses, SRY induces SOX9 in Sertoli cells, resulting in formation of testes with seminiferous tubules, interstitial Leydig cells and peritubular myoid cells. Meanwhile XX fetuses without SRY develop ovaries. In cattle, most XX heifers born with a male twin, so-called freemartins, develop nonfunctioning ovaries and genitalia with an intersex phenotype. Interestingly, freemartins sometimes develop highly masculinized gonads with seminiferous tubule-like structures despite the absence of SRY. However, in these cases, the degree of masculinization in each gonadal somatic cell type is unclear. Here, we report a rare case of a freemartin Japanese black calf with almost complete XX sexreversal. Gross anatomical analysis of this calf revealed the presence of a pair of small testis-like gonads with rudimentary epididymides, in addition to highly masculinized genitalia including a pampiniform plexus, scrotum and vesicular gland. Histological and immunohistochemical analyses of these masculinized gonads revealed well-defined seminiferous tubule-like structures throughout the whole gonadal parenchyma. In epithelia of these tubules, SOX9-positive supporting cells (i.e., Sertoli cells) were found to be arranged regularly along the bases of tubules, and they were also positive for GDNF, one of the major factors for spermatogenesis. 3β-HSD-positive cells (i.e., Leydig cells) and SMA-positive peritubular myoid cells were also identified around tubules. Therefore, for the first time, we found the transdifferentiation of ovarian somatic cells into all testicular somatic cell types in the XX freemartin gonads. These data strongly support the idea of a high sexual plasticity in the ovarian somatic cells of mammalian gonads.

Natural exceptions to normal gonad development in mammals

Gonads are the only organs with 2 possible developmental pathways, testis or ovary. A consequence of this unique feature is that mutations in genes controlling gonad development give rise not only to gonadal malformation or dysfunction but also to frequent cases of sex reversal, including XY females, XX males and intersexes. Most of our current knowledge on mammalian sex determination, the genetic process by which the gonadal primordia are committed to differentiate as either testes or ovaries, has derived mainly from the study of sex-reversed mice obtained by direct genetic manipulation. However, there are also numerous cases of natural exceptions to normal gonad development which have been described in a variety of mammals, including both domestic and wild species. Here, we review the most relevant cases of: (1) natural, non-induced sex reversal and intersexuality described in laboratory rodents, including Sxr and B6-Y(DOM) mice; (2) sex reversal in domestic animals, including freemartinism in bovids and pigs, XX sex reversal in pigs, goats and dogs, XY sex reversal in the horse, and sex chromosome chimerism and sex reversal in the cat, and (3) sex reversal in wild mammals, including the generalised true hermaphroditism described in talpid moles, XY sex reversal in Akodon, Microtus and Dicrostonyx species, males lacking a Y chromosome and SRY in Ellobius lutescens, the X* chromosome of Myopus schisticolor, and sex chromosome mosaicism and X0 females in Microtus oregoni. These studies are necessary to elucidate particular aspects of mammalian gonad development in some instances and to understand how the genetic mechanisms controlling gonad development have evolved.

Low levels of X-inactive specific transcript in somatic cell nuclear transfer embryos derived from female bovine freemartin donor cells

The present study compared developmental potential, telomerase activity and transcript levels of X-linked genes (HPRT, MECP2, RPS4X, SLC25A6, XIAP, XIST and ZFX) in bovine somatic cell nuclear transfer (SCNT) embryos reconstructed with cells derived from a freemartin (female with a male co-twin) or from normal female cattle (control). The rates of cleavage, development to blastocyst and hatched blastocyst stage, and the mean numbers of total and inner cell mass cells in the freemartin SCNT embryos were not significantly different from those of control SCNT embryos (p > 0.05). The levels of telomerase activity analyzed by RQ-TRAP in the freemartin SCNT embryos were also similar to those of the normal SCNT embryos. Transcript levels of HPRT, MECP2, RPS4X and XIAP, measured by quantitative real-time RT-PCR, were not significantly different between the control and freemartin SCNT embryos (p > 0.05). However, the transcript levels of SLC25A6, XIST and ZFX were significantly decreased in the freemartin SCNT embryos compared to control SCNT embryos (p < 0.05). Transfer of 71 freemartin SCNT embryos to 22 recipient cows resulted in 4 (18%) pregnancies, which were lost between days 28 and 90 of gestation. Taken together, the present study demonstrates that the transcript levels of several X-linked genes, especially XIST, showed an aberrant pattern in the freemartin SCNT embryos, suggesting aberrant X inactivation in freemartin clones which may affect embryo survival.

Ovarian aging: mechanisms and clinical consequences

Menopause is the final step in the process referred to as ovarian ageing. The age related decrease in follicle numbers dictates the onset of cycle irregularity and the final cessation of menses. The parallel decay in oocyte quality contributes to the gradual decline in fertility and the final occurrence of natural sterility. Endocrine changes mainly relate to the decline in the negative feedback from ovarian factors at the hypothalamo-pituitary unit. The declining cohort of antral follicles with age first results in gradually elevated FSH levels, followed by subsequent stages of overt cycle irregularity. The gradual decline in the size of the antral follicle cohort is best represented by decreasing levels of anti-Mullerian hormone. The variability of ovarian ageing among women is evident from the large variation in age at menopause. The identification of women who have severely decreased ovarian reserve for their age is clinically relevant. Ovarian reserve tests have appeared to be fairly accurate in predicting response to ovarian stimulation in the assisted reproductive technology (ART) setting. The capacity to predict the chances for spontaneous pregnancy or pregnancy after ART appears very limited. As menopause and the preceding decline in oocyte quality seem to have a fixed time interval, tests that predict the age at menopause may be useful to assess individual reproductive lifespan. Especially genetic studies, both addressing candidate gene and genome wide association, have identified several interesting loci of small genetic variation that may determine fetal follicle pool development and subsequent wastage of his pool over time. Improved knowledge of the ovarian ageing mechanisms may ultimately provide tools for prediction of menopause and manipulation of the early steps of folliculogenesis for the purpose of contraception and fertility lifespan extension.

Sex chromosome chimerism and the freemartin syndrome in Rideau Arcott sheep

In cattle, nearly all heifers born co-twin to a male are freemartins, XX/XY chimeras that exhibit a characteristic masculinized phenotype. However, in sheep, while litters containing males and females are common, freemartins are relatively rare. The primary aim of this study was to determine the frequency and features of XX/XY chimerism in female Rideau Arcott sheep. Also, breeding records were used to investigate the effect of litter size and sex ratios, as well as the genetic basis of the condition. Finally, the migration and transcriptional competence of cells of the opposite sex in the XX/XY female and male chimeras was explored. Genomic DNA (gDNA) from peripheral blood cells of ewes was screened by PCR for the male-specific SRY gene. Of 230 lambs screened, 10 were identified as chimeras. Litter size and sex ratio showed no statistically significant effect on the frequency of chimerism. PCR and FISH analysis confirmed the presence of opposite sex cells in female and male chimeras, and in the case of ewes, their migration to tissues other than blood. Transcriptional activity of SRY and AMH was detected in gonads of ewes, whereas XIST expression was detected in white blood cells of chimeric rams. It was concluded that the frequency of sex chromosome chimerism in Rideau Arcott sheep is estimated at 4.35%, with no significant effect of litter size and sex ratio. Moreover, as it was shown that opposite sex cells can migrate to tissues other than blood and be transcriptionally active in chimeric sheep, we speculate on the role they can play in these animals.

Evaluation of anti-Müllerian hormone as a test for the prediction of ovarian reserve

OBJECTIVE

To compare in an integral way the value of the basal serum anti-Müllerian hormone (AMH) level with most of the established ovarian reserve tests.

DESIGN

Prospective randomized controlled trial.

SETTING

Fertility center of a university hospital in the Netherlands.

PATIENT(S)

One hundred ten patients undergoing their first IVF cycle who were randomized, by a computer-designed four-block system, into two groups.

INTERVENTION(S)

Fifty-six patients underwent a clomiphene citrate challenge test (CCCT), and 54 patients underwent an exogenous FSH ovarian reserve test (EFORT). In all patients, basal AMH, basal FSH, basal inhibin B, antral follicle count (AFC), and basal volume of the ovaries were measured. In all patients, the test was followed by a standard IVF treatment.

MAIN OUTCOME MEASURE(S)

Ovarian response after ovarian hyperstimulation in an IVF treatment, expressed as the total number of stimulated follicles, retrieved oocytes, and ongoing pregnancies.

RESULT(S)

The best prediction of ovarian reserve (Y) was seen in a multiple regression prediction model that simultaneously included AFC, inhibin B increment in the EFORT, and basal volume of the ovaries. Univariate logistic regression showed that the best predictors for poor response were AMH, the CCCT, basal FSH, and the AFC. For hyperresponse, univariate logistic regression showed that the best predictor was AFC. Multiple logistic regression analysis did not produce a better model in terms of improving the prediction of poor response or hyperresponse. The best predictors for the prediction of non-pregnancy were the CCCT and the E(2) increment in the EFORT.

CONCLUSION(S)

Anti-Müllerian hormone is comparable with other commonly used ovarian reserve tests but is probably most applicable in general practice.

Anti-Müllerian hormone receptor defect

Anti-Müllerian hormone (AMH), produced by gonadal somatic cells, is mainly responsible for the regression of Müllerian ducts--the anlagen of uterus and Fallopian tubes--during male sex differentiation. Like other members of the transforming growth factor beta (TGF-beta) family, AMH signals through two serine/threonine kinase receptors, of which type II is specific, and type I is shared with the bone morphogenetic protein family. Persistent Müllerian duct syndrome is a rare form of male pseudohermaphroditism characterized by the persistence of Müllerian derivatives in otherwise normally virilized males. It is transmitted according to a recessive autosomic pattern and is due, in 84% of cases, to mutations of AMH and AMH receptor type II genes. Serum AMH is normal for age in patients with AMH type II mutations and low or undetectable in those with AMH mutations. In 14% of cases the origin of the condition is unknown.

Freemartinism in river buffalo: clinical and cytogenetic observations

During the last five years forty phenotypic female river buffalos with reproductive problems and two phenotypic male co-twins of females, raised in the provinces of Caserta and Salerno (southern Italy) underwent cytogenetic investigation. Of the 42 animals studied, 10 freemartins (8 females and 2 males) were found with variable percentages of male and female blood cells, the majority however showing similar percentages of both. Of the eight females, six showed normal body conformation, vagina and clitoris, while two showed some male traits (tight pelvis). The two males were apparently normal with only a reduced size of one testicle in one animal. Clinical observations performed in the internal reproductive organs of the female carriers by both rectal palpation (5 females) and direct observation after mating (3 females) revealed serious damages varying from complete lack of internal sex adducts (closed vagina) to hypoplasia of Mullerian ducts and absence (or atrophy) of ovaries. All freemartin females were sterile. To our knowledge, this is the first detailed description of freemartinism in river buffalo by combining clinical and cytogenetic analyses.

Predicting time of parturition from changing vaginal temperature measured by data-logging apparatus in beef cows with twin fetuses

Vaginal temperatures (VT) of crossbred (Japanese Black crossed Holstein-Friesian) beef cows (n = 31) were measured by a data-logging apparatus to obtain serial data from days 0 to 6 before parturition. For both single and twin pregnancies, no significant differences were observed in VT during days 3-6 before parturition. Maternal VT was not affected by maternal weight just after parturition, parity, fetal sex, or total fetal litter weight. Average of twin litter weights for two males (MM) and two females (FF) had the strong positive correlations (r = 0.84; P < 0.05) with maternal VT, whereas twin weights of mixed-gender twins (FM) did not correlate with maternal VT (r = -0.26; P = 0.61). Maternal temperature decreased as weights of the female fetus of FM twins became heavier (r = -0.82; P < 0.05). In contrast, maternal VT of FF and MM twins increased as twin weights increased. We defined when the VT began to decrease before parturition by two different methods. One was the "same hours method" where differences in VT between a particular time of day and the corresponding time of the preceding day were compared when the VT was consistently > or =0.3 or > or =0.5 degrees C for more than 3h. The second method was the "maximum-minimum method" where decreased in the maximum or the minimum values of the day over > or =0.3 and > or =0.5 degrees C were compared to values of preceding day. Onset of decreased VT before expulsion was not different between singletons and twins. In an attempt to define the critical condition in predicting parturition, we estimated assumable predicting probability using the 31 cows that were collected VT. When the parturition occurred within 60 h in the "same hours method" and 72 h since VT was > or =0.3 degrees C and in the "maximum-minimum method", the assumable probability was 100%. In verification experiment under these condition, the "same hours method" had a higher probability of predicting the time of parturition than the "maximum-minimum method", and it was possible to detect the onset of decreased VT at the correct time by the minutes. We concluded that "same hours method" was useful for predicting parturition time in cattle with single and twin pregnancies by the serial measurement of vaginal temperature.

Persistent differences in the level of chimerism in B versus T cells of Freemartin cattle

Parabiosis during pregnancy regularly results in an exchange of hematopoietic stem cells between cattle twins. We have exploited this phenomenon and show differences in the levels of chimerism between the descendant cell types. Female recipients were screened for the levels of male donor contribution in surface IgM-bearing B lymphocytes versus CD3(+) T lymphocytes using immunomagnetic fractionation and Y-chromosome specific in situ hybridization. Two calves of 15 were discovered to have less than 10% of B cells but over 70% of T cells and other blood leukocytes of male origin. The donor cell ratios remained stable for 9 months. Analysis of lymphoid tissues revealed a similar cell type specific pattern of male cell ratios in both female calves and one twin brother. These findings are in agreement with the existence of an essentially self-sufficient population of developing B cells that gives rise to the peripheral pool of B lymphocytes in young cattle.

Limited Contribution of Circulating Cells to the Development and Maintenance of Nonhematopoietic Bovine Tissues

Bone marrow-derived stem cells appear surprisingly multipotent in experimental settings, but the physiological significance of such plasticity is unclear. We have used sex-mismatched cattle twins with stably chimeric hematopoietic systems to investigate the general extent of integration of circulating cells to the nonhematopoietic cell lineages in an unmanipulated large mammal. The donor-derived (Y+) nonhematopoietic cells in female recipient tissues were visualized by Y-chromosome specific in situ hybridization combined with pan-leukocyte labeling. Y+ leukocytes were frequent in all tissues, but in 11 of 12 animals, average contribution to nonhematopoietic lineages was in any tissue below 1% (in brain <0.001%). Significantly higher integration rate was detected in regenerating granulation tissue. Also, one animal showed a high frequency of nonhematopoietic Y+ cells in several tissues, including intestinal epithelium and mammary gland stroma. In conclusion, circulating cells do not appear significant in the development and maintenance of nonhematopoietic bovine tissues, but may be important in regeneration and other special conditions.

AMH induces mesonephric cell migration in XX gonads

Migration of mesonephric cells into XY gonads is a critical early event in testis cord formation. Based on the fact that anti-Müllerian hormone (AMH) can induce testis cord formation in XX gonads, we investigated whether AMH plays a role in the induction of cell migration. Addition of recombinant AMH induced mesonephric migration into XX gonads in culture. AMH-treated XX gonads displayed increased vascular development and altered morphology of the coelomic epithelium, both features of normal testis differentiation. AMH did not induce markers of Sertoli or Leydig cell differentiation. We examined early testis development in Amh-deficient mice, but found no abnormalities, suggesting that any function AMH may have in vivo is redundant. Other transforming growth factor (TGF-beta) family proteins, bone morphogenetic proteins (BMP2 and BMP4) show similar inductive effects on XX gonads in culture. Although neither BMP2 nor BMP4 is expressed in embryonic XY gonads, our findings suggest that a TGF-beta signalling pathway endogenous to the XY gonad may be involved in regulation of mesonephric cell migration. The factors involved in this process remain to be identified.

Age dependent changes in plasma anti-Müllerian hormone concentrations in the bovine male, female, and freemartin from birth to puberty: relationship between testosterone production and influence on sex differentiation

To understand the behaviour of the gonads, in terms of hormonal secretion, in a model of intersexual development naturally occurring in mammals, we determined plasma concentrations of testosterone, progesterone, and anti-Müllerian hormone (AMH) in bovine freemartins, and compared them to normal levels measured in males and females from birth to puberty. We found that newborn males and freemartins have very high concentrations of AMH (over 700ng/ml). Conversely, plasma AMH concentration is always below 120ng/ml in females. While values remain stable in males for the first five months of life, they sharply decrease in the freemartins within the first fortnight, and reach female levels, which demonstrates that AMH is essentially originated in the male twin. In young bulls the trend of plasma testosterone concentrations is opposite to that of the AMH. The rise in testosterone production at puberty corresponds to a sharp decline in AMH concentrations. Bovine plasma concentrations of AMH are surprisingly higher than those measured in other mammals, including man and mouse. The results obtained are discussed in reference to comparative aspects of endocrine functions.

Oligoclonal Peyer's patch follicles in the terminal small intestine of cattle

In small ruminants, the development of B cells differs from that in mice or in man. The anti-body repertoire is expanded in the Peyer's patches of the terminal ileum where each B-cell follicle is found by a few cells. To investigate the amount of founder clones in bovine ileal follicles, we have used sex mismatched cattle twins. These animals are chimeric due to placental anastomoses. Y-chromosome targeted in situ hybridization was used to trace donor-derived cells of the male genotype in a female recipient (called a freemartin). A strong clustering of lymphoid cells originating from either twin was seen in the ileal Peyer's patches (IPPs). Furthermore, the follicles displayed a low amount of immunoglobulin heavy chain gene configurations in comparison with the splenic or jejunal follicles. These findings strongly suggest that as in sheep, the B-cell follicles in cattle IPPs develop oligoclonally.

Ontogenesis of female-to-male sex-reversal in XX polled goats

The association of polledness and intersexuality in domestic goats (PIS mutation) made them a practical genetic model for studying mammalian female-to-male sex reversal. In this study, gonads from XX sex-reversed goats (PIS-/-) were thoroughly characterized at the molecular and histologic level from the first steps of gonadal differentiation (36 days post coitum [dpc]) to birth. The first histologic signs of gonadal sex reversal were detectable between 36 and 40 dpc (4-5 days later than the XY male) and were mainly characterized by the reduction of the ovarian cortex and the organization of seminiferous cords. As early as 36 dpc, aromatase (CYP19) gene expression was decreased in XX (PIS-/-) gonads, whereas genes normally up-regulated in males, such as SOX9 and AMH, showed an increased expression level from 40 dpc. Thereafter, steroidogenic cell precursors were affected, and at 56 dpc, WNT4 and 3beta-HSD were expressed in a male-specific manner in sex-reversed gonads. Another noticeable feature was a progressive disappearance of germ cells, clearly visible in testicular cords around 70 dpc where 50-75% of germ cells were absent in XX (PIS-/-) gonads. These observations indicated that the causal mutation of PIS acts very early in the sex-determining cascade and affects primarily the supporting cells of the gonad.

Gonadal development in mammals at the cellular and molecular levels

In mammals, although sex is determined chromosomally, gonads in both sexes begin development as similar structures. Until recently it was widely held that female development constituted a "default" pathway of development, which would occur in the absence of a testis-determining gene. This master gene on the Y chromosome, SRY in the human and Sry in the mouse, is thought to act in a cell-autonomous fashion to determine that cells in the gonadal somatic population develop as pre-Sertoli cells. Triggering of somatic cell differentiation along the Sertoli cell pathway is therefore a key event; it was thought that further steps in gonadal differentiation would follow in a developmental cascade. In the absence of Sertoli cells, the lack of anti-Mullerian hormone would allow development of the female Mullerian duct and absence of Leydig cells would prevent maintenance of the Wolffian duct. Recent findings that female signals not only maintain the Mullerian duct and repress the Wolffian duct but also suppress the development of Leydig cells and maintain meiotic germ cells, together with the finding that an X-linked gene is required for ovarian development and must be silenced in the male, have shown that the female default pathway model is an oversimplification. Morphological steps in gonadal differentiation can be correlated with emerging evidence of molecular mechanisms; growth factors, cell adhesion, and signaling molecules interact together, often acting within short time windows via reciprocal control relationships.

Birth of a Holstein freemartin calf co-twinned to a schistosomus reflexus fetus

An unusual case of a live Holstein freemartin calf co-twinned with schistosomus reflexus fetus is presented here. Delivery of the schistosomus reflexus was achieved by fetotomy 24 h after manual delivery of a live heifer calf. The dam subsequently experienced concurrent metritis and left displacement of the abomasum; however, she conceived following insemination 85 d post partum. Cytogenetic examination of the live heifer using lymphocyte culture and cutaneous fibroblast cell culture failed to demonstrate chromosomal chimerism, whereas polymerase chain reaction (PCR) detected the presence of the bovine Y-chromosome marker BRY-1. Low concentrations of testosterone, estradiol and progesterone at 3, 6, 24 and 48 h after administration of hCG were detected in the serum of the freemartin heifer. Genetic, hormonal, histological and clinical findings established the live female co-twin calf was a freemartin, an abnormality of phenotypic sex. Failure to detect any significant peripheral concentrations of androgen supports the hypothesis that masculinization of the freemartin reproductive tract arises from diffusion of androgen and possibly other substances from the male co-twin rather than from endogenous production of androgen within the freemartin. This report documents that the freemartin condition can be induced by a male fetus with severe developmental abnormalities.

XX germ cells: the difference between an ovary and a testis

In mammals, gonadal sex is determined by the action of the testis-determining gene, SRY. In the absence of SRY, the indifferent gonad follows an alternative pathway and develops as an ovary. Both mitotic and meiotic germ cells appear to play an essential role in ensuring ovarian development. Ovaries depleted of germ cells before or after ovarian differentiation has commenced can develop seminiferous cords, suggesting that XX germ cells may inhibit testicular differentiation in the ovary.

Gonadal sex reversal of the developing marsupial ovary in vivo and in vitro

Undifferentiated tammar wallaby ovaries were transplanted under the skin of male pouch young during the period of mitotic division of the XX germ cells. After 25 days, all the germ cells had disappeared and the ovaries contained seminiferous-like cords. Similarly, undifferentiated ovaries cultured for 4 days with recombinant human Mullerian-inhibiting substance (rhMIS) also contained well-differentiated seminiferous-like cords and few or no surviving germ cells. The majority of controls cultured without rhMIS developed as normal ovaries. However, in a few control ovaries seminiferous-like cords developed in those regions of the ovaries that were partially necrotic and contained few germ cells. These results strongly suggest that sex-reversal of the tammar ovary is the direct result of loss of mitotic germ cells, rather than an effect of MIS on female somatic cells. MIS is apparently toxic to these female germ cells in mitosis, but not to male germ cells in mitosis. Thus, in normal development in the tammar, the presence of XX germ cells in the ovary inhibits the formation of seminiferous cords so that the gonad develops as an ovary.

The ovary retains male potential after the thermosensitive period for sex determination in the turtle Emys orbicularis

Emys orbicularis is a turtle with temperature-dependent sex determination. The thermosensitive period (TSP) lies between embryonic stages 16 and 22. Gonadal differentiation begins during this period involving oestrogens. Treatment with oestrogens during TSP results in the differentiation of ovaries at a male-producing temperature (25 degrees C), whereas treatment with an antioestrogen (tamoxifen) or with nonsteroidal aromatase inhibitors results in gonadal masculinization at a female-producing temperature (30 degrees C). The present study examines the effects on the ovary of inhibiting aromatase activity after TSP. Eggs of E. orbicularis incubated at 30 degrees C were given five or seven applications of 10 micrograms aromatase inhibitor Letrozole (CGS 20267) in ethanol, between stages 22+ and 24-25 when ovarian aromatase activity strongly increases. Individuals which received five applications were sacrificed at stages 24(+)-25. Those which received seven applications were sacrificed either at stage 25+ (close to hatching), or 34-36 days after hatching. Gonadal aromatase activity and related gonadal structure were studied in each individual. In the three series, the gonadal aromatase activity in individuals treated with Letrozole varied from similar or close to that in controls to much lower, and the gonadal structure varied from ovary-like to ovotestis. Ovotestes had the lowest levels of aromatase activity, under 4 fmoles/h/gonad, close to testis levels. They were found in 7 out of 26 individuals given Letrozole. Besides ovotestes, gonads presenting various degrees of masculinization, with enlarged epithelial cords and lacunae in the medulla, were found. Therefore, by inhibiting aromatase activity and thus estrogen synthesis, we were able to obtain the differentiation of testis-like cords or tubes in ovaries of E. orbicularis, after the period of temperature sensitivity. These results show that the ovary retains male potential after this period. Thus, besides their implication during the critical embryonic period for gonadal sex differentiation, oestrogens play a role in maintaining the ovarian structure after this period. A decrease in oestrogen levels could explain some other cases of ovarian masculinization known in vertebrates.

H-Y antigens

H-Y antigen is defined as a male histocompatibility antigen that causes rejection of male skin grafts by female recipients of the same inbred strain of rodents. Male-specific, or H-Y antigen(s), are also detected by cytotoxic T cells and antibodies. H-Y antigen appears to be an integral part of the membrane of most male cells. In addition, H-Y antibodies detect a soluble form of H-Y that is secreted by the testis. The gene (Smcy/SMCY) coding for H-Y antigen detected by T cells has been cloned. It is expressed ubiquitously in male mice and humans, and encodes an epitope that triggers a specific T-cell response in vitro. Additional epitopes coded for by different Y-chromosomal genes are probably required in vivo for the rejection of male grafts by female hosts. The molecular nature of H-Y antigen detected by antibodies on most male cells is not yet known. Testis-secreted, soluble H-Y antigen, however, was found to be identical to Müllerian-inhibiting substance (MIS). MIS cross-reacts with H-Y antibodies and identical findings were obtained for soluble H-Y antigen and MIS, i.e., secretion by testicular Sertoli and, to a lesser degree, ovarian cells, binding to a gonad-specific receptor, induction of gonadal sex reversal in vitro and, in cattle, in vivo. H-Y antisera also detect a molecule or molecules associated with the heterogametic sex in nonmammalian vertebrates. Molecular data on this antigen or antigens are not yet available.

Cellular localization of müllerian inhibiting substance messenger ribonucleic acid during human ovarian follicular development

Müllerian inhibiting substance is expressed in the human reproductive system and has been associated with oocyte meiotic arrest. In situ hybridization was used to selectively localize ovarian cells containing high levels of müllerian inhibiting substance messenger ribonucleic acid, a müllerian inhibiting substance precursor, during different stages of human follicular development. Müllerian inhibiting substance transcript was noted in the granulosa cells of primordial, primary, and antral follicles. Surprisingly, transcript was also identified within the cytoplasm of oocytes and throughout the ovarian stroma. Controls included sense oligoprobe, positive and negative tissue controls, and treatments minus the detection antibody. Localization of transcript within the cytoplasm demonstrates that active transcription of müllerian inhibiting substance messenger ribonucleic acid occurs within both fetal and adult human female gonads. The presence of müllerian inhibiting substance messenger ribonucleic acid within oocyte cytoplasm could implicate an autocrine role for müllerian inhibiting substance-derived peptides in the establishment of oocyte competence.

New insights on the mechanism of testis differentiation from the morphogenesis of experimentally induced testes in genetically female chick embryos

Embryonic testes grafted in the extraembryonic coelom of 3-day-old genetically female chick embryos may induce total and definitive reversal of gonadal sex differentiation. In this experimental condition, the left gonad becomes a testis instead of an ovary. This makes it possible to compare testicular and ovarian morphogenesis in animals having the same genetic sex and to discount what is due to differences in the genetic determination between male and female. The morphogenesis of such testes is marked by a disappearance of the cortical germinal epithelium. The medullary sex cords keep a narrow lumen instead of becoming large lacunae. The germ cells remain few in the sex cords and do not become meiotic. Furthermore, interstitial cell development is known to be very slow. As a consequence the gross size of the gonad is much smaller than that of an ovary. All these morphogenetic phenomena are unlike those observed during normal ovarian differentiation and evidence an inhibiting influence of the grafted testes. Since inhibition and masculinization are concomitant, inhibition appears to be the mechanism responsible for gonadal sex reversal. The extraembryonic situation of the grafted testes and their relation with the embryo only via the blood stream demonstrates the role of a secreted substance or substances still to be exactly identified. Previous data suggest that this could be the anti-Müllerian-hormone (AMH). Furthermore, previous and present results show that testis differentiation can be actively induced in a bird. This does not agree with the hypothesis that the gonads of the homogametic sex, i.e., the testes in birds, do not need any inducer in order to differentiate.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-müllerian hormone: hormone or growth factor?

Anti-Müllerian hormone (AMH) is a dimeric glycoprotein member of the TGF-beta family. It is synthesized by immature Sertoli cells, and, to a lesser degree, by adult Sertoli and granulosa cells. AMH is responsible for the regression of Müllerian ducts in the male fetus; it also has deleterious effects on the female fetal reproductive tract, destroying Müllerian primordia and germ cells, and masculinizing the fetal ovary on the rare occasions female fetuses become exposed to its effects. All other suggested actions for AMH--retardation of oocyte meiosis, inhibition of EGF receptor autophosphorylation, anti-cancer activity--have been reported with crude hormone preparations, and have not been confirmed using pure AMH. Its relatively limited sphere of action--the fetal genital tract--and the fact that it is secreted into the general circulation and can act at long range, imply that AMH is more like a hormone than a growth factor, but the complex interaction between hormones and growth factors make a formal distinction impossible.

Anti-Müllerian hormone produces endocrine sex reversal of fetal ovaries

We have previously reported that anti-Müllerian hormone (AMH), also known as Müllerian-inhibiting substance, the testicular glycoprotein involved in regression of the Müllerian ducts of the male fetus, induces the formation of seminiferous cord-like structures in fetal ovaries exposed to it in organ culture. We have now investigated the effect of bovine AMH, purified to homogeneity, on ovarian endocrine differentiation. Ovine fetal ovaries exposed to AMH release testosterone instead of estradiol, an endocrine sex reversal due to suppression of aromatase activity. AMH dramatically decreases the conversion rate of testosterone to estradiol and also decreases total aromatase activity, as measured by the tritiated water technique. AMH acts by decreasing aromatase biosynthesis rather than by blocking enzyme activity, as suggested by the relatively long period of AMH exposure required to produce an effect. In the rabbit fetal ovary, aromatase activity is AMH-responsive during the whole gestational period. The basal steroidogenic activity of rat fetal ovaries is extremely low but can be markedly increased by cAMP. AMH completely blocks the effect of cAMP. Taken together, our results suggest that AMH plays a pivotal role in both morphological and endocrine gonadal sex differentiation.

Role of mammalian Y chromosome in sex determination

It has long been assumed that the mammalian Y chromosome either encodes, or controls the production of, a diffusible testis-determining molecule, exposure of the embryonic gonad to this molecule being all that is required to divert it along the testicular pathway. My recent finding that Sertoli cells in XX----XY chimeric mouse testes are exclusively XY has led me to propose a new model in which the Y acts cell-autonomously to bring about Sertoli-cell differentiation. I have suggested that all other aspects of foetal testicular development are triggered by the Sertoli cells without further Y-chromosome involvement. This model thus equates mammalian sex determination with Sertoli-cell determination. Examples of natural and experimentally induced sex reversal are discussed in the context of this model.

Secretion of the anti-müllerian hormone by the gonads of experimentally sex reversed female chick embryos

The gonads of genetically female chick embryos experimentally transformed into testes under the influence of a embryonic testis graft are able to induce in vivo the regression of Müllerian ducts when they are grafted to female embryonic hosts. On the other hand female gonads only transformed into ovotestes are ineffective on the host MDs, as in the case for female gonads. These results show that totally sex reversed gonads have the same properties as a normal testis. In particular they produce the anti-Müllerian hormone, whereas partially reversed gonads do not or only do at a very low level.